In recent years, the brain science and medial measurement technologies have made remarkable progress. For the purpose of collecting intracerebral information, various kinds of sensing devices and new techniques for imaging cerebral functions have been realized. Intracerebral information measuring devices can be roughly divided into invasive and noninvasive types. Invasive devices require a certain kind of surgery, such as the incision of the scalp or skull of the subject, in order to bring an electrode or similar element in direct contact with the brain. On the other hand, noninvasive devices are designed to indirectly access the brain from outside the subject's head (i.e. through the scalp or skull) to extract certain kinds of intracerebral information.
Many reports have been made on the invasive intracerebral information measuring devices, such as the “Michigan” electrode (developed at the University of Michigan, USA) or the “Utah” electrode (developed at the University of Utah). These electrodes can be used to perform multi-point measurements at the level of cellular size inside the brain. Another example is an intracranial electrode manufactured by a Japanese company, UNIQUE MEDICAL CO., LTD. (Refer to Non-Patent Document 1.) This electrode is officially authorized in Japan as a device for the clinical therapy of epilepsy.
These conventional types of invasive intracerebral information measuring devices are basically designed to be mounted on a brain of the subject after the brain is exposed by incising the skull. Particularly, when the measurement needs to be performed over a wide area of the brain, it is necessary to incise an accordingly large area of the skull. Any surgery including the incision of the skull inherently requires a major operation and hence imposes significant strain on the subject. Furthermore, it is accompanied by high risk of infection or the like.
On the other hand, for the noninvasive measurement of cerebral functions, excellent measurement techniques have been developed, such as the f-MRI (functional magnetic resonance imaging) or optical topography. These techniques have made considerable achievements in the fields of diagnosis and research. For example, the optical topography measurement is capable of measuring the change in a local blood volume in the brain of the subject. Such a technique is useful for the diagnosis of cerebrovascular disease (for example, refer to Patent Document 1). However, due to the restriction that the noninvasive measurement is merely an indirect measurement, it is difficult to improve the resolution, sensitivity or other performances of the measurement. Another problem is that, although the information obtained at a region near the surface of the brain is relatively accurate, it is difficult to obtain information at deeper regions of the brain.